The present invention relates to a lithographic printing machine and a lithographic printing method. More specifically, the present invention relates to a lithographic printing machine capable of forming an image-forming layer on a plate cylinder for imaging of the lithographic printing machine, forming an image pattern on the image-forming layer by scanning exposure of an image by laser beams on the basis of digital data, making a printing plate, and capable of effecting printing excellent in resistance against scumming with the same printing plate on the same printing machine, and relates to a method of lithographic printing.
Lithographic printing is a method of effecting printing by making use of an ink-receptive lipophilic area and an ink-nonreceptive hydrophilic or lipophobic area, and photosensitive lithographic printing plate precursors (PS plates) are now widely used as printing plate materials.
PS plates comprising a metal support such as an aluminum plate having been subjected to surface-graining treatment, anodizing treatment and hydrophilization treatment having provided thereon a photosensitive layer comprising a photosensitive diazo resin, a photopolymerizable composition, a photo-crosslinkable composition, etc., have been put to practical use and are prevailingly used. The photosensitive layer of the nonimage area of these PS plates is removed by image exposure and development, and printing is performed by making use of the hydrophilicity of the support surface and the lipophilicity of the photosensitive layer of the image area.
Further, so-called direct plate-making of directly making an offset printing plate from the original without using a film for plate-making is going into the field of general offset printing by making use of characteristics such as simplicity requiring no skill, labor saving, rapidity capable of expediting plate-making, etc. In particular, in recent years, various printing plate materials of novel types have been developed conjointly with the rapid progress of output systems, e.g., a pre-press system, an image setter, a laser printer, etc.
These printing plate materials have the possibilities of application to so called plate-making on machine, i.e., plate-making by installing these printing plate materials on the plate cylinder of a printing machine and imagewise irradiating them with laser beams to make a printing plate. However, direct plate-making which requires development process with a developing solution is not good for plate-making on machine.
As the printing plate precursor which requires no development process, there is disclosed in WO 99/37481 an ablation type positive lithographic printing plate precursor capable of recording by laser, which comprises a support having provided thereon a crosslinked hydrophilic layer, and thereon an ink-receptive surface layer of an organic polymer layer which contains one or more polymers and light/heat converting dyes capable of absorbing radiation of lasers, and the polymer layer absorbs radiation by ablation.
Furthermore, as the trend of plate-making, direct plate-making on the same printing machine as that for printing work by the above-described lithographic printing machine of direct imaging on printing machine is proposed. For example, it is suggested in JP-A-9-99535 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) to use a seamless cylinder (hence there is no space or groove) in place of plate cylinders so far been used for offset printing, cure a curable polymer coated on the seamless cylinder, and convert the affinity to a printing ink of the surface of the polymer by selectively irradiating the polymer surface with a laser. Since only the surface of the polymer is selectively converted by laser irradiation, the thickness and the uniformity of the polymer coating matter little. A plate cylinder is cleaned after one printing work is finished. There is described in the patent specification that the cleaning need not be perfect because the surface of a plate cylinder itself is not exposed to ink.
Such direct plate-making on printing machine has been developed for the purpose of providing a reusable surface layer which does not necessitate perfect cleaning of coating by the method of tolerating the remaining coating on the plate cylinder for imaging after cleaning and shortening the time required to make an image again, hence the method has the advantage of heat mode plate-making and printing method. However, with respect to heat mode sensitivity to irradiated laser rays, the above technique is not sufficient yet and, from the viewpoint of practical use, it has further been desired to achieve higher sensitization, to thereby increase a discriminating effect of an image area and a nonimage area (a discriminating property of hydrophobic property/hydrophilic property before and after exposure), and a method of direct plate-making on machine providing printed matters with no scumming.
Accordingly, an object of the present invention is to provide a lithographic printing machine which makes it possible to directly form an image and make a printing plate on machine, to sufficiently maintain the discrimination of an image area and a nonimage area, and to provide printed matters without generating scumming even under severe printing conditions. Another object is to provide a lithographic printing method.
As a result of eager investigations for achieving the above objects, the present inventors have found that printed matters generating no scumming even under severe printing conditions can be obtained using a polymer having a functional group which is converted from hydrophilic to hydrophobic by heating or by the heat generated by light/heat conversion as the heat-sensitive material for forming the image-forming layer (which is also referred to as a radiation-sensitive layer sometimes) on a lithographic printing machine equipped with a plate cylinder for imaging. Thus, the present invention has been achieved.
That is, the present invention is as follows.
(1) A lithographic printing machine comprising a plate cylinder for imaging, a blanket cylinder, an impression cylinder, and a film-coating unit, a film-hardening unit, an imaging unit and a cleaning unit each unit of which is adjacent to the plate cylinder for imaging, wherein an image-forming layer containing a polymer having a functional group which is crosslinked by light or heat before imaging and a functional group which is converted from hydrophilic to hydrophobic by the heat generated by infrared ray irradiation is formed by the coating unit.
(2) A lithographic printing method on a lithographic printing machine comprising a plate cylinder for imaging, a blanket cylinder, an impression cylinder, and a film-coating unit, a film-hardening unit, an imaging unit and a cleaning unit each unit of which is adjacent to the plate cylinder for imaging, which comprises the steps of at least (a) cleaning operation of cleaning said plate cylinder for imaging, (b) coating operation of coating an image-forming layer containing a polymer having a functional group converting from hydrophilic to hydrophobic by heating on the surface of said plate cylinder for imaging, (c) hardening operation of hardening said image-forming layer to a solid state, and (d) surface conversion operation of forming an image pattern due to hydrophilic/hydrophobic conversion corresponding to the digital data to be printed on the surface of said image-forming layer.
According to the present invention, a printing plate can be made directly from digital data by the process comprising the steps of forming, as a radiation-sensitive material, a thin layer of a polymer having a functional group converting from hydrophilic to hydrophobic by heating or by the heat generated by light/heat conversion on the surface of the plate cylinder for imaging of a printing machine by means of a film-coating unit and a film-hardening unit each unit of which is adjacent to the plate cylinder, and recording with a thermal head or a laser radiating infrared rays equipped in the imaging unit.
The radiation-sensitive layer according to the present invention largely converts from hydrophilic to hydrophobic to exhibit polarity conversion by scanning exposure of an image with laser beams in short time. As a result, the discrimination against inks occurs and an image area and a nonimage area are formed, thus a printing plate capable of providing printed matters not generating scumming can be made directly on machine without requiring special processes such as wet development or rubbing after image exposure even under severe printing conditions.
In general, special care should be taken in film hardening about the storage stability after coating of radiation-sensitive materials, but in the present invention it is not necessary to give care to the storage stability, since hardening treatment can be performed immediately after direct coating on machine, thus the radiation-sensitive material of the present invention is suitable to direct plate-making on machine.